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Abstract

The title compound, C27H31N3, has E substitution at each imine double bond where the two N atoms adopt a trans–trans relationship. The benzene rings are twisted out of the mean plane of the pyridine ring; the mean planes of the aromatic groups are rotated by 63.0 (1) and 72.58 (8)°. The crystal structure is sustained mainly by C—Hπ and hydro­phobic methyl–methyl inter­actions.

Acknowledgments

The authors thank FONACIT–MCT, Venezuela, for financial support (project LAB-199700821)

supplementary crystallographic
information

Comment

The development of new ligand politopics bearing nitrogen heterocyclic units has
been receiving increasing interest in the coordination chemistry of
transition-metal based homogeneous catalysis (Togni & Venanzi, 1994). In this
context, the planar tridentate–or potentially bidentate–ligand
2,6-bis(imino)pyridine and its derivatives (Orrell et al., 1997) have
attracted great attention and the bis(arylimino)pyridine ligand
[2,6-(ArN?CR)2C5H3N] by (Alyea & Merrel, 1974). There are several recent
examples of reactions catalyzed by complexes bearing the ligand
2,6-bis(arylimino)pyridine ligands such as epoxidation of olefins (Çetinkaya
et al., 1999), cyclopropanation of styrene (Bianchini et al.,
2000). Specially, it has been nearly a decade since sterically demanding
bis(arylimino)pyridine ligands were found to impart transitions metals, iron
and cobalt, catalytic activities for olefin polymerization (Small & Brookhart,
1998; Britovsek et al., 1999). Many reports have appared in the
literature concerning the effects (sterically and/or electronic) of ligand
modifications, to find a structure–activity relationships. The crystal
structure of different 2,6-bis(arylimino)pyridine ligands and their transition
metal complexes offer the possibilty to compare directly structural
parameters. Here we report the synthesis and crystal structure of the title
compound, (I), (Fig. 1).

The molecule adopts a nonplanar conformation in which an E configuration around
each C?N imine group is observed, likewise the two N atoms display a
trans-trans relationship. The conformation of the system N–N–N
system is of course different in each case. In general, X-ray structures of
bis(arylimino)pyridines reveal that in the solid state the imino nitrogen
atoms prefer to be disposed trans with respect to the central pyridine
nitrogen (Mentes, et al. 2001; Huang et al., 2006) in order to
minimize the interaction between the nitrogen lone pairs. The phenyl rings in
(I) are twisted out of the mean plane of the pyridine ring, the mean planes of
C8–C13 and C19–C24 being rotated by 63.0 (1)° and 72.58 (8)°, respectively.
This molecular conformation is determined by the formation of pairs of
intramolecular C—H···N hydrogen bonds, involving methyl groups with the N of
the pyridine ring and isopropyl groups with imine groups with a range of
distances C···N = 2.799 (3)–2.892 (4) Å (Fig. 2). These interactions lead to
the formation of five-membered rings described by graph-set simbol S(5)
(Bernstein et al., 1995).

The crystal structure of (I) consists of dimers linked by self-complementary
C—H···π interactions related by an inversion centre C15···Cg1 =
3.757 Å; were Cg1 is the centroid of the N1,C1–C5 ring (Fig. 2).
Neighbouring dimers are connected through additional C—H···π between phenyl
rings (Fig. 3), generating supramolecular sheets parallel to the c
axis. Details of geometrical parameters of these hydrogen bonding interactions
are summarized in Table 2. Finally, the stacking of adjacent sheets is
sustained by hydrophobic methyl-methyl interactions along the a axis
(Fig. 4).

Special details

Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes)
are estimated using the full covariance matrix. The cell e.s.d.'s are taken
into account individually in the estimation of e.s.d.'s in distances, angles
and torsion angles; correlations between e.s.d.'s in cell parameters are only
used when they are defined by crystal symmetry. An approximate (isotropic)
treatment of cell e.s.d.'s is used for estimating e.s.d.'s involving l.s.
planes.

Refinement. Refinement of F2 against ALL reflections. The weighted R-factor
wR and goodness of fit S are based on F2, conventional
R-factors R are based on F, with F set to zero for
negative F2. The threshold expression of F2 >
σ(F2) is used only for calculating R-factors(gt) etc.
and is not relevant to the choice of reflections for refinement.
R-factors based on F2 are statistically about twice as large
as those based on F, and R- factors based on ALL data will be
even larger.